Fibonnacci is better known under the name of Leonard of Pisa. Fibonnacci was born in the Italian town of Pisa, but soon joins his father in the Algerian colony of Pisa Bujania, where he learns the basics of arithmetic. At about the age of 20, Fibonnacci being a businessman travels to all the large cities of the Mediterrean of the time and learns Indian numbering and Arabian calculus. He widens his knowledge by making other voyages. He uses this experience to improve accounting methods, which he needed to complete his studies in classical mathematics, such as Euclidean geometry. Near the end of this life, Fibonnacci visits the court of Emperor Frederick II. In 1240, The Republic of Pisa decides to issue Fibonnacci a monthly salary, which demonstrates the importance accorded to his work and perhaps to the work he did for the public administration of the city. His works: only several works still exist today. His most important, Liber Abaci, Book of the Abacus, which appeared in 1202, reveals a precocious knowledge of Indian and Arabian numbering systems, of number theory and of practical mathematical and financial problems, of complex algebraic problems. In other works, Fibonnacci deals with negatives numbers and starts the work in approximating the number Pi.